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Abstract:
Offered the choice between two monetary rewards, most people would prefer $10 today over
$12 in a week, while only few would prefer $10 in a year over $12 in a year and a week.
Many behavioral studies so far found that humans behave dynamically inconsistent and
irrationally when making such monetary decisions called intertemporal choices.
Psychological theories assume that special cognitive processes take place only when
immediate gratification is possible, leading to such preference reversals. Self-theories suggest
that these processes are special in decision making for oneself. Choices made for another
person should not elicit the same processes and thus are assumed to be made in a more
consistent manner regardless of immediacy. If this assumption holds true, it would have a
high impact on explaining mechanisms important in decision delegation processes.
In our first experiment, we investigated brain activation and choice behavior when
intertemporal choices were made for oneself and for another, unknown person. We found that
when an immediate reward was included in the choice set, intertemporal choices made for
oneself were accompanied by activation in highly emotion- and reward-related areas, such as
the pregenual anterior cingulate cortex, and the ventral striatum. However, none of these areas
showed elevated activation when making such choices for another person. While this is in
accordance with our hypothesis concerning the brain correlates of intertemporal choices for
self and other, we did not find any behavioral differences in the choices the participants made
for themselves and others: In both cases subjects inconsistently chose the smaller, but
sooner, reward more often if it was available immediately.
To investigate these discrepancies between choice and neural activation in detail, we splitted
our sample into two groups, depending on subjects' individual discount values. Within the
group of subjects who discounted future rewards more strongly, we could find the same
differences in brain activation patterns between self and other as before. In accordance with
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these brain activation differences, we also found behavioral differences between decisions for
self and other in this group of strongly discounting subjects: They more often chose the larger,
later reward for the other person than for themselves. This shows that at least subjects who
discounted future rewards very strongly for themselves chose less impulsively for others.
In our second study we investigated another variable influencing brain activation during such
intertemporal choices: passivity. Can humans keep a “cool head” while watching what is
decided for them without having any possibility to intervene?
We used the same paradigm, this time letting our participants only observe choices being
made for them or for another person. We found greater activity in the inferior frontal junction,
intraparietal sulcus, and precuneus when participants observed choices yielding immediate
compared to delayed rewards, for both self and other. A conjunction analysis with experiment
1 yielded that contrary to experiment 1, neither when making choices for oneself nor when
making choices for another person, activation differences in the pregenual anterior cingulate
cortex (pACC) and ventral striatum were found, indicating no differential involvement of
these areas in today and delay trials when choices were observed. We concluded that
immediate rewards were also special here, but relying on a more general mechanism, because
their reception could not be actively influenced.
